The invention relates to a method of producing a dielectric having a perowskite structure comprising perowskite-forming compounds consisting of stoichiometric alkaline earth titanates, alkaline earth zirconates, alkaline earth stannates and mixed crystals thereof, wherein an admixture of eutectic-forming compounds which in practice cannot be built into the perowskite lattice is added to the perowskite lattice, and wherein the mixture of compounds is sintered at a partial oxygen pressure from 0.2 to 1 Bar in the temperature range from 1000.degree.-1250.degree. C. Such a method is the subject of U.S. Pat. application Ser. No. 24,811 which is hereby incorporated by reference into the present specification.
The above-mentioned Patent Application describes a method for reducing the sintering temperature of alkaline earth titanates, -zirconates and -stannates or the mixed crystals thereof to such an extent that the physical and, particularly, the dielectric properties of the sintered bodies are maintained, but the manufacturing process for producing these sintered bodies becomes cheaper and simpler. This object is achieved by adding an admixture of eutectic-forming compounds which form CuO.Cu.sub.2 O or CuO.Cu.sub.2 O.Me.sup.IV O.sub.2 when sintered in an oxygen atmosphere and which in practice cannot be built into the perowskite lattice of the stoichiometric perowskite compound, where Me.sup.IV O.sub.2 is at least an oxide of an element of group IV of the Periodic System of Elements, and by sintering the mixture of compounds at a partial oxygen pressure of 0.2 to 1 Bar in the temperature range from 1000.degree.-1250.degree. C.
As a rule, dense ceramics of barium titanate (BaTiO.sub.3) and the mixed crystals thereof with other perowskites cannot be sintered below 1300.degree. C. and in special cases only at approximately 1400.degree. C. The low porosity of 3 to 5% and less, required for a dielectric ceramic, are reached at these high sintering temperatures only.
For dielectric ceramics the microstructure is, however, equally as important as the porosity. To obtain an optimal dielectric constant either a very fine-grained microstructure or a very coarse-grained micro-structure is required, depending on the material. Alternatively, it may be possible that, depending on the use, the same material is required in a coarse-grained as well as in a fine-grained microstructure. It is therefore very important that the grain growth can be influenced in a reliable manner to the one or the other direction. A pronounced grain growth is not observed except at elevated temperatures. For example, with undoped barium titanate (BaTiO.sub.3), that is to say pure barium titanate, and the mixed crystals thereof, a coarse-grained microstructure is not obtained until after the addition of a slight excess of TiO.sub.2 above a sintering temperature of approximately 1320.degree. C. Small deviations of this approximate value are met in starting materials of a technical purity.